Study On Passivation Of Available Cadmium In Tobacco-growing Soil

Studies on the behaviors of Cd and techniques for remediation of Cd-polluted soils had been payedmuch attention. In situ immobilization of Cd in contaminated soils was a cost-effective and environmentally friendly remediation technique. In this study, lime, red mud, sepiolite and acticarbon were used for passivator materials, the cadmium adsorption desorption characteristics and main influencing factors had been studied. In cadmium polluted planting tobacco soil, four different kinds of passivator with different amount were added on field experiments. The discussions of the study included:Four kinds of passivator in field conditions influence on heavy metal cadmium content in the soil, and reduction of heavy metal cadmium in tobacco leaves, and observed the after effect of passivator. The main results were as follows:1. The adsorption of Cd on passivator materials was mainly affected by contact time,initial concentration of Cd, pH of reaction solution and concentration of ions. It was found that a contact time of 40 min was necessary for the adsorption to reach equilibrium. Quasi secondary dynamics equation model could better fitting to passivator on Cd adsorption kinetics, Langmuir equation could be suitable for simulating the isothermal adsorption of Cd.The calculation of lime, red mud, sepiolite and acticarbon theoretical maximum Cd adsorption ion respectively 3463, 2958, 3058, 1897 mg/kg. When the solution pH value was 2,acticarbon adsorption of Cd decreased significantly, only 11.4% of the equilibrium adsorption quantity, increased gradually with the increase of solution pH, lime, red mud, sepiolite on Cd adsorption quantity changed little. As with the increase of ionic strength, inhibited passivator on Cd adsorption. With 0.01 mol/L CaCl2 as desorption agent, lime and red mud of desorption rate were low, desorption rate of sepiolite and acticarbon were up to 20%.2. Application of lime and sepiolite could significantly increase the soil pH, but red mud had no significant effect, application of acticarbon to a certain extent reduced the soil pH.Application of passivator could effective state of cadmium content in soil, effect of theproportion of the sepiolite and acticarbon were best; at the same time reduced the Cd content in tobacco leaves, the effect was followed by sepiolite > lime >acticarbon > red mud. State NH4 Ac extraction of cadmium in soil and tobacco leaf in the Cd content was significantly positive correlation. Passivator agent into the soil after the first year of time was to a certain degree of passivation effect, reduced the effectiveness of Cd in soil biological, through the experiment for three consecutive years, the effect of passivator gradually weakened.